Throughout this application, various publications are referenced by arabic numerals within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed in this application.
Cyclosporine A (CsA) is a cyclic undecapeptide of fungal origin which is an immunosuppressive agent useful in preventing organ rejection in transplant patients (1-3).
Because the therapeutic index of CsA is narrow, it is important to measure serum cyclosporine levels in patients treated with CsA (4). This can be accomplished by high performance liquid chromatography or by RIA, with the latter procedure being the more convenient one.
It has been reported, and we have confirmed (unpublished), that CsA, itself, is non-immunogenic (5). To obtain antibodies, therefore, it is necessary to link CsA to a protein carrier. The side chains of CsA, however, consist only of aliphatic groups with none of the functional groups customarily used to link a hapten to a carrier. Previous workers have made immunogenic cyclosporine C (CsC)-protein conjugates because CsC has a threonine residue in position 2 (5). Linkage to a protein was via a hemisucciniate, using a water soluble carbodiimide as a coupling agent. Polyclonal antisera were successfully raised in this way and are routinely used to measure CsA in patients sera (5). More recently, monoclonal antibodies were prepared using an activated ester of a lysyl-CsA derivative (6).
We have chosen to use CsA, itself, as a hapten by converting it to a reactive carboxyl-containing peptide via a photochemical reaction. Coupling of this derivative to proteins has led to the successful raising of CsA-specific rabbit antibodies that can be used to measure CsA levels in sera of transplant patients under treatment with CsA.